I can't help you with the 300RUM, but I can offer you this one bit of advice.
Make darn sure you thoroughly clean your bore before you switch bullets and repeat the process before switching back. The jacket material between the two is completely different & can foul VERY badly if you mix them together (ask me how I know
). Other than that, Tikkamike has some data floating around here for the LRX & Retumbo, do a search.
Let us know how it shoots.